Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code or other information. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise have a surface attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means.
RFID devices include active tags and labels, which include a power source for broadcasting signals, and passive tags and labels, which do not. In the case of passive devices, in order to retrieve the information from the chip, a “base station” or “reader” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The RFID reader receives and decodes the information from the RFID tag. In general, RFID tags can retain and communicate enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as to those to which information is written only once (although the information may be read repeatedly), and those to which information may be written to repeatedly during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
RFID devices further can be characterized as passive, semi-passive, and active RFID devices. Passive RFID devices have no internal power supply. Power for operation of passive RFID devices is provided by the energy in an incoming radio frequency signal received by the device. Most passive RFID devices signal by backscattering the carrier wave from an RF reader. Passive RFID devices have the advantage of simplicity and long life, although performance of them may be limited.
There are at least two approaches to assembling RFID devices having IC chips with antennas and/or other electronic components. The IC chips are manufactured on a wafer and are typically delivered as a sawn wafer. The antennas which may be printed, etched or die cut are provided on a flexible web. In the first approach, manufacturers use precision pick-and-place machines to bond and electrically connect the bare IC chips directly to the other device components (e.g., antenna) without any intermediate connecting leads. These electronic components are placed into the substrate circuitry in a single process.
The second route of RFID assembly uses an intermediate connection lead instead of bonding bare dies directly onto the substrates. This is because as the chips become smaller, the process of interconnecting IC chips with antennas becomes more difficult. Thus, to interconnect the relatively small IC chips to the antennas in RFID inlays, intermediate structures variously referred to as “strap leads,” “interposers,” and “carriers” are sometimes used to facilitate inlay manufacture. The intermediate structures include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling the chips to the antennas. These leads provide a larger effective electrical contact area between the chips and the antenna than do the contact pads of the chip alone. With the use of the intermediate structures, the alignment between an antenna and a chip does not have to be as precise during the direct placement of the chip on the antenna as without the use of such strap leads.
Regardless of how the chip is attached to the antenna, either directly or through a strap, one issue that is encountered during the use of the RFID tag is when the label (i.e., substrate) is attached to a package and the label does not lie or remain on a completely flat surface. As the labels are bent, the die/antenna juncture is subject to stress and is prone to fracturing and breaking. In addition, the antenna may also be subject to bending and having its functionality compromised thereby. For example, the antenna may become detached from the substrate as the label bends. The same issues occur when the RFID tag is attached to an article that is subject to bending, such as an article of clothing or fabric material. Other bendable materials include sheets of plastic or metal. Moreover, the IC can be simply knocked off during the application of the RFID tag to the article or during subsequent processing such as during the step of printing the label.
Accordingly, there is a long-felt, but as yet unsatisfied need in the RFID device manufacturing field to be able to produce RFID devices that address the deficiencies noted above.